Hi Graham Matthews,
Capital gains tax is worked out differently. The lower capital gain rate of 18% and the higher rate of 28% remain unchanged.
Private residence relief is set againt the amount subject to capital gains, thus reducing the amount taxed at 18% and or 28%.
There is a calculator at
Tax when you sell your home which would help you calculate the gain.
You may also be able to claim a foreign tax credit for any overseas capital gains tax paid.
Thank you.